What’s Vulnerable › Vulnerabilities

CVE-2026-63994: tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]()

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-19 · updated 2026-10-19
• Weakness: CWE-416

Description

In the Linux kernel, the following vulnerability has been resolved: tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]() Sashiko found that iptunnel_pmtud_build_icmp() and iptunnel_pmtud_build_icmpv6() were caching ip_hdr() and ipv6_hdr() before an skb_cow() call which can reallocate skb->head. Fix this possible UAF by initializing the local variables after the skb_cow() call. Remove skb_reset_network_header() calls which were not needed.

Affected products

• Linux kernel: from 5.9 before 5.10.259; from 5.11 before 5.15.210; from 5.16 before 6.1.176; from 6.2 before 6.6.143; from 6.7 before 6.12.93; from 6.13 before 6.18.35 — fixed in 5.10.259, 5.15.210, 6.1.176, 6.12.93, 6.18.35, 6.6.143

How to fix

Upgrade to a fixed version: Linux kernel 5.10.259, 5.15.210, 6.1.176, 6.12.93. Check the vendor advisory for mitigations.

References

• https://git.kernel.org/stable/c/50750d86a2e5266aba0c295483b3397843198b11
• https://git.kernel.org/stable/c/6dff77899b9e9fe5d854abda3a98ad04e7229ef7
• https://git.kernel.org/stable/c/7254aef4d1a7e18e887af9010e2f2dc34806789b
• https://git.kernel.org/stable/c/76cd9398a0470257ab765bdf5f358a2af2e17934
• https://git.kernel.org/stable/c/95b6d772bfe788331d9742d73eaa12e113b2adc4
• https://git.kernel.org/stable/c/b4bc94353050b1fa7b702bd4c6600710dd926cff
• https://git.kernel.org/stable/c/bf8b3f34c37c162357138e7c0942723b8b94fed1
• https://git.kernel.org/stable/c/f3f204541f280a6ecb04503a0d6794d93990ca43

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